Learn about the cryptically named “M-theory,” a development that requires a total of 11 dimensions.

The final episode shows how in 1995 Edward Witten of Princeton’s Institute for Advanced Study, aided by others, revolutionized string theory by successfully uniting the five different versions into a single theory that is cryptically named “M-theory,” a development that required a total of 11 dimensions. But the new 11^th dimension is different from all the others, since it implies that strings can come in higher dimensional shapes called membranes, or “branes” for short. These possess truly science-fiction-like qualities, since in principle they can be as large as the universe. A brane can even be a universe — a parallel universe — and we may be living in one right now.